High reactance transformer



Oct. 15, 1957 J. R. CLARK 2,810,113

HIGH REACTANCE TRANSFORMER Filed Dec. 29, 1954 [Hz/enter;

James R. 692%", [39 772's fitter/76y United rates li atent HIGHREACTANCE rnANsronMun James lit. Clark, Fort Wayne, Ind, assignor toGenerai Electric Company, a corporation of New York Appiication December29, 1054, Serial No. 478,379

12 Claims. (Cl. 336-165) This invention relates to high reactancetransformers, and more particularly to high reactance transformers ofthe unbalanced, midpoint grounded secondary windingtype.

High reactance transformers are commonly used for starting and operatingarc discharge devices, such as luminous tubes. Arc discharge devices arecharacterized by their negative resistance characteristic, i. e., theirresistance decreases as the current flow therethrough in creases. A highinitial voltage is thus needed to break down or start the device,followed by a requirement for a high impedance in the circuit in orderto limit the current flow to a value which will not destroy the device.The high reactance or leakage transformer is ideally suited for thisdual purpose since it provides a high open circuit voltage for startingthe device and high inductive reactance to limit the current flow afterthe device has started.

Luminous tubes, such as neon tubes of the type commonly used in signs,are generally cold-cathode type devices, i. e., no means for pre-heatingthe cathodes of the device to aid starting are provided. Thus, quitehigh open circuit voltages, i. e., frequently on the order of 1,000 to15,000 volts, are required for starting. In order to reduce the safetyhazards attendant with such high voltages, and also to reduce theinsulation requirements of the transformer, high reactance transformershave in the past been constructed with the midpoint of the secondarywinding grounded, thus providing an arrangement wherein the maximum opencircuit voltage to ground is only one-half the open circuit terminalvoltage of the secondary winding.

Two types of high reactance, midpoint grounded secondary windingtransformers have been provided; balanced and unbalanced. In thebalanced type, a secondary winding coil is physically located on eitherside of the primary winding, while in the unbalanced type, bothsecondary winding coils are physically located on one side of theprimary. The balanced type construction is satisfactory from aperformance standpoint, however, two magnetic shunts are required forleakage flux, whereas only one is required in the unbalanced type ofconstruction. Thus, from an economic standpoint, the industry haspreferred the unbalanced type of construction.

In the past, in the unbalanced type of construction, the two coils ofthe secondary winding have had the same number of turns. In thisconstruction, however, one secondary coil is more loosely coupled to theprimary winding than the other secondary winding coil. When the turns ofthe two coils are equal, the more loosely coupled coil has higherinductive reactance than the more closely coupled coil. Thus, when themore closely coupled coil is short circuited to ground while the moreloosely coupled coil is open circuited, a higher short circuit currentflows due to the lower inductive reactance of the more closely coupledcoil than flows when the more loosely coupled coil is short circuited toground with the more closely coupled coil open circuited. Since thetransformer must be designed to withstand the short circuit current ofeither secondary winding coil Without overheating, heavier wire must beprovided in the more closely coupled coil; this in turn requires morewinding space and thus a larger core. It is thus seen that in theunbalanced midpoint grounded secondary winding high reactancetransformer with an equal number of turns in both secondary coils, morecopper and iron is required than would be necessary for normaloperation, in order to provide for the high short circuit current in themore closely coupled secondary winding coil.

It is therefore desirable to provide an unbalanced, midpoint groundedsecondary winding high reactance transformer in which the short circuitcurrent of the more closely coupled secondary winding is made morenearly equal to the Short circuit current of the moreloosely coupledsecondary winding coil thus reducing theamount of copper and ironrequired.

It is therefore an object of this invention to provide an improved highreactance transformer incorporating the desirable features set forthabove.

This invention in its broadest aspects, provides a high reactancetransformer comprising a core formed of magnetic material with a primarywinding arranged thereon adapted to be connected to a source ofalternating current. A first secondary winding coil is arranged on thecore loosely coupled to the primary winding and a second secondarywinding coil is also arranged on the core more loosely coupled to theprimary winding than the first secondary winding coil. One end of eachof the secondary winding coils is connected to a ground and the otherends of the secondary winding coils are respectively adapted to beconnected to an arc discharge device, the secondary winding coils beingconnected in additive voltage relationship in order to providesufficient open circuit voltage for starting the device. In order tomake the short circuit current of both coils more nearly equal, the moreclosely coupled secondary winding coil is provided with more turns thanthe more loosely coupled secondary winding coil. This increases theinductive reactance of the more closely coupled secondary winding coiland reduces the short circuit current sufficiently to permit a reductionin wire size with an accompanying saving in copper and iron.

In the drawing,

Fig. 1 illustrates an unbalanced, midpoint grounded secondary windinghigh reactance transformer incorporating this invention;

Fig. 2 illustrates another type of unbalanced, midpoint groundedsecondary winding high reactance transformer incorporating thisinvention; and

Fig. 3 is a schematic illustration of the transformers of Figs. 1 and 2.

Referring now to Fig. 1, there is shown a high reactance transformergenerally identified as 1 having a core 2 formed of a stacked pluralityof relatively thin laminations of magnetic material. Core 2 comprises acenter winding leg 3 and a pair of outer yoke members 4 and 5. Yokemembers 4 and 5 are respectively provided with end legs 6 and 7 whichabut the ends of center winding leg 3, and shunts 8 respectivelyintermediate the end legs 6 and 7. Shunts 8 define primary windingwindows 9 with end legs 6 and secondary Winding windows 10 with end legs7. Shunts 8 are spaced from center winding legs 3 by airgaps 11 thusproviding a high reluctance path for leakage flux.

A primary winding 12 is arranged on center winding leg 3 of core 2 inprimary winding windows 9 and has its leads 13 and 14 adapted to beconnected to an external source of alternating current (not shown). Afirst secondary winding coil 15 is arranged on center winding leg 3 insecondary winding windows 10 adjacent shunts 8 and a second secondarywinding coil 16 is arranged on center winding leg 3 in secondary windingwindows adjacent end legs 7. The ends 17 and 18 of secondary windingcoils and 16 are connected to a ground, which connection is preferablymade to the core 2, as at 19. The other ends and 21 of secondary windingcoils 15 and 16 are respectively adapted to be connected to operate anarc discharge device 22, as shown in Fig. 3. Secondary winding coils 15and 16 are connected in additive voltage relationship in order toprovide the requisite open circuit voltage for starting arc dischargedevice 22, which may be a luminous tube such as a neon tube.

It will be readily seen that in the embodiment of Fig. 1, the secondarywinding coil 16 is more loosely coupled to the primary winding 12 thanis the other secondary winding coil 15. Thus, if the secondary windingcoils 15 and 16 were provided with an equal number of turns, secondarywinding coil 16 would have a higher inductive reactance and thus theshort circuit current in the more closely coupled secondary winding coil15 with its end 20 short circuited to ground would be higher than theshort circuit current in the more loosely coupled secondary winding coil16 with its end 21 short circuited to ground. In order to make theseshort circuit currents more equal, the more closely coupled secondarywinding coil 15 is provided with more turns than the more looselycoupled secondary winding coil 16. It has been found that with the moreclosely coupled secondary winding coil 15 having between approximately10 and 30 percent more turns than the more loosely coupled secondarywinding coil 16, the short circuit current of coil 15 is reduced toapproximately the value of the short circuit current of coil 16. It ofcourse will be readily apparent that the optimum design in which theshort circuit currents would be equal will difier with each transformerdesign, however, the determination of the relationship of the turns ofthe two secondary windings to achieve complete equality of short circuitcurrents is well Within the skill of the art.

Referring now to Fig. 2, in which like elements are indicated by likereference numerals, there is shown a slightly different physicalarrangement in which secondary winding coil 16 is wound over secondarywinding coil 15. Here again, secondary winding coil 16 is more looselycoupled to primary winding 12 than is secondary winding coil 15.

A comparison will now be made between the high reactance transformer ofthe type shown in Fig. I having an equal number of turns in thesecondary winding coils and a high reactance transformer constructed inr accordance with this invention. A transformer having a primary windingcoil with approximately 474 turns andsecondary winding coils each havingapproximately 11,000 turns when connected as shown in Fig. 3, providedan open circuit voltage of 5,000 volts with 115 volts, 60 cycles appliedto the primary coil. With the more closely coupled secondary windingcoil 15 short circuited to ground, the short circuit current in coil 15was 66.6 milliamperes while the short circuit current when the moreloosely coupled secondary winding coil 16 was short circuited to groundwas 45.0 milliamperes. This shows that with an equal number of turns, onsecondary winding coils 15 and 16, the short circuit current in the moreclosely coupled. secondary winding coil is much higher than the shortcircuit current in the more loosely coupled secondary winding coil. Atransformer constructed in accordance with this invention was thentested again having a primary'winding with approximately 474 turnsconnected to a 115 volt, 60 cycle source of alternating current. Theopen. circuit secondary voltage of this transformer was again 5,000volts, however, the more closely coupled secondary winding coil 15 hadapproximately 12,100 turns while the more loosely coupled secondarywinding. coil 16 had approximately 9,950 turns. The ratio of coil turnswas thus; 1 to 1.22,- or

coil 15 had 22 percent more turns than coil 16. With this construction,the short circuit current of the closely coupled secondary winding coil15 was found to be 56.4 milliamperes while the short circuit current ofthe more loosely coupled secondary winding coil 16 was found to be 48.0milliamperes. It is thus seen that while the short circuit current ofthe more loosely coupled secondary winding coil 16 has been increasedonly 3 milliamperes, the short circuit current of the more closelycoupled secondary winding coil has been reduced over 10 milliarnperes.The short circuit currents of the two coils could be made substantiallyequal by slightly increasing the number of turns on the more closelycoupled secondary winding coil 15 and slightly decreasing the number ofturns on the more loosely coupled secondary winding coil 16. In theparticular example given, the short circuit current of the more closelycoupled secondary winding coil 15 was reduced a suflicient amount topermit substantial savings in copper and iron while the open circuitsecondary voltages of each secondary winding coil were still within 15percent of one-half the overall open circuit secondary voltage, thuspermitting the transformer to still be referred to as a midpointgrounded secondary device.

It will now be readily apparent that this improved construction byreducing the short circuit current of the more closely coupled secondarywinding coil permits the design of unbalanced, midpoint groundedsecondary winding type high reactance transformers having smaller wirein the more closely coupled secondary winding coil thus permittingsavings in both copper and iron. It will also be readily seen that thisimproved construction provides the same operating characteristics in asmaller, more compact, and less expensive device.

While I have illustrated and described particular embodiments of thisinvention, further modifications and improvements will occur to thoseskilled in the art. I desire that it be understood, therefore, that thisinvention is not limited to the forms shown and I intend in the appendedclaims to cover all modifications within the spirit and scope of thisinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core looselycoupled to said primary winding, and a second secondary winding coil onsaid core more loosely coupled to said primary winding than said firstsecondary winding coil, one end of each of said secondary winding coilsbeing connected to a ground, leads for respectively connecting the otherends of said secondary winding coils to an arc discharge device, saidsecondary winding coils being connected in additive voltagerelationship, said first secondary winding coil having more turns thansaid second secondary winding coil whereby the short circuit currents ofeach of said secondary winding coils when the other coil is opencircuited are approximately equal.

2. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core looselycoupled to said primary winding, and a second secondary winding coil onsaid core more loosely coupled to said primary winding than said firstsecondary winding coil, one end of each of said secondary winding coilsbeing connected to aground, leads for respectively connecting the otherends of said secondary winding coils to an arc discharge device, saidsecondary winding coils being connected in additive voltagerelationship, said first secondary winding. co'il having at least- 10*percent more turns than saidsecond secondary winding coil whereby theshort circuit currents of each of said secondary winding coils when theother coil is open circuited are approximately equal.

3. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core looselycoupled to said primary winding, and a second secondary winding coil onsaid core more loosely coupled to said primary winding than said firstsecondary winding coil, one end of each of said secondary winding coilsbeing connected to a ground, leads for respectively connecting the otherends of said secondary winding coils to an arc discharge device, saidsecondary winding coils being connected in additive voltagerelationship, said first secondary winding coil having to 30 percentmore turns than said second secondary winding whereby the short circuitcurrents of each of said secondary winding coils when the other coil isopen circuited are approximately equal.

4. A high reactance transformer for starting and operating an arcdischarge device comprising 'a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary Winding, and a second secondary winding coil on saidcore on the side of said first secondary winding coil remote from saidprimary winding, said core being arranged to provide a path for leakageflux, one end of each of said secondary winding coils being connected toa ground, leads for respectively connecting the other ends of saidsecondary winding coils to an arc discharge device, said secondarywinding coils being connected in additive voltage relationship, saidfirst secondary winding coil having more turns than said secondsecondary winding coil whereby the short circuit currents of each ofsaid secondary winding coils when the other coil is open circuited areapproximately equal.

5. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, and a second secondary winding coil on saidcore on the side of said first secondary Winding coil remote from saidprimary winding, said core being arranged to provide a path for leakageflux, one end of each of said secondary winding coils being connected toa ground, leads for respectively connecting the other ends of saidsecondary winding coils to an arc discharge device, said secondarywinding coils being connected in additive voltage relationship, saidfirst secondary winding coil having at least 10 percent more turns thansaid second secondary winding coil whereby the short circuit currents ofeach of said secondary winding coils when the other coil is opencircuited are approximately equal.

6. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, and a second secondary winding coil on saidcore on the side of said first secondary winding coil remote from saidprimary winding, said core being arranged to provide a path for leakageflux, one end of each of said secondary winding coils being connected toa ground, leads for respectively connecting the other ends of saidsecondary winding coils to an arc discharge device, said secondarywinding coils being connected in additive voltage relationship, saidfirst secondary winding coil having 10 to 30 percent more turns thansaid second secondary winding coil whereby the short circuit currents ofeach of said secondary winding coils when the other coil is opencircuited are approximately equal.

7. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, said core having a high reluctance magnetishunt for leakage flux disposed between said primary winding and saidfirst secondary winding coil, and a second secondary Winding coil onsaid core on the side of said first secondary winding coil remote fromsaid primary winding, one end of each of said secondary winding coilsbeing connected to a ground, leads for respectively connecting the otherends of said secondary winding coils to an arc discharge device, saidsecondary winding coils being connected in additive voltagerelationship, said first secondary winding coil having more turns thansaid second secondary winding coil whereby the short circuit currents ofeach of said secondary winding coils when the other coil is opencircuited are approximately equal.

8. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, said core having a high reluctance magneticshunt for leakage flux disposed between said primary winding and saidfirst second winding coil, and a second secondary winding coil on saidcore on the side of said first secondary winding coil remote from saidprimary winding, one end of each of said secondary winding coils beingconnected to a ground, leads for respectively connecting the other endsof said secondary winding coils to an arc discharge device, saidsecondary winding coils being connected in additive voltagerelationship, said first second winding coil having at least 10 percentmore turns than said second secondary winding coil whereby the shortcircuit currents of each of said secondary winding coils when the othercoil is open circuited are approximately equal.

9. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary Winding coil on said core spacedfrom said primary winding, said core having a high reluctance magneticshunt for leakage flux disposed between said primary winding and saidfirst secondary winding coil, and a second secondary winding coil onsaid core on the side of said first secondary winding coil remote fromsaid primary winding, one end of each of said secondary winding coilsbeing connected to a ground, leads for respectively connecting the otherends of said secondary winding coils to an arc discharge device, saidsecondary winding coiis beingconnected in additive voltage relationship,said first secondary winding coil having 10 to 30 percent more turnsthan said second secondary winding coil whereby the short circuitcurrents of each of said secondary winding coils when the other coil isopen circuited are approximately equal.

10. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, said core having a high reluctance magneticshunt for leakage flux disposed between said primary winding and saidfirst secondary winding coil, and a second secondary winding coil woundover said first secondary winding coil, one end of each of saidsecondary winding coils being connected to a ground, leads forrespectively connecting the other ends of said secondary winding coilsto an arc discharge 7 device, said secondary Winding coils beingconnected in additive voltage relationship, said first secondary Windingcoil having more turns than said secondary Winding coil whereby theshort circuit currents of each of said secondary winding coils when theother coil is open circuited are approximately equal.

11. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating current, a first secondary winding coil on said core spacedfrom said primary winding, said core having a high reluctance magneticshunt for leakage flux disposed between said primary Winding and saidfirst secondary winding coil, and a second secondary winding coil woundover said first secondary winding coil, one end of each of saidsecondary Winding coils being connected to a ground, leads forrespectively connecting the other ends of said secondary winding coilsto an arc discharge device, said secondary winding coils being connectedin additive voltage relationship, said first secondary winding coilhaving at least 10 percent more turns than said second secondary windingcoil whereby the short circuit currents of each of said secondarywinding coils when the other coil is open circuited are approximatelyequal.

12. A high reactance transformer for starting and operating an arcdischarge device comprising a core formed 8 of magnetic material, aprimary winding on said core adapted to be connected to a source ofalternating cur rent a first secondary Winding coil on said core spacedfrom said primary winding, said core having a high reluctance magneticshunt for leakageflux disposed between said primary winding and saidfirst secondary winding coil, and a secondary secondary winding coilwound over said first secondary winding coil, one end of each of saidsecondary winding coils being connected to a ground, leads forrespectively connecting the other ends of said secondary Winding coilsto an arc discharge device, said secondary winding coils being connectedin additive voltage relationship, said first secondary winding coilhaving 10 to 30 percent more turns than said sec- 0nd secondary windingcoil whereby the short circuit currents of each of said secondarywinding coils when the other coil is open circuited are approximatelyequal.

References Cited in the file of this patent UNITED STATES PATENTS1,777,256 Daley et a1. Sept. 30, 1930 1,786,422 Daley Dec. 30, 19302,183,355 Mauerer Dec. 12, 1939 2,382,638 Keiser et al Aug. 14, 194-5FOREIGN PATENTS 415,803 Italy Nov. 2, 1946

